James Morrison

Contents, Test Results, and Data Availability for GSC 1.2

A collaboration between STScI and ARI has produced a new astrometric reduction of the Guide Star Catalog (GSC, Lasker et al. 1990). This new version, GSC 1.2, has dramatically reduced the systematic errors present in GSC 1.1. The positions in GSC 1.1 are affected by plate-based systematic distortions which are largest at the plate edges (1.0″, north; 1.2″, south) (Taff et al. 1990a). These positions also suffer from systematic errors which are a function of magnitude and radial distance from the plate center (Morrison et al. 1996). This effect is small for radii under 2.7° from the plate center, then rapidly increases producing an average offset of the faint stars (15m) versus the reference stars (10m) of 0.9″ at the plate edges.

The Guide Star Catalog and the Digitized Sky Survey as Resources for other Surveys

In contemplating the planning and implementation. of all-sky survey missions — either from the ground, such as DENIS and 2MASS. or from space. such as GAIA — it is useful to recall that an important part of observational astronomy has historically been the creation of catalogs containing the reference and program objects required to support such observing programs. As the technological complexity and cost of large-scale astronomical projects has increased dramatically over the last decades, so has the demand to provide the best scientific return for these investments by optimizing observing efficiency, which in turn depends on the use of proper pointing and input catalogs.